To obtain desired information existing on a network such as the Internet by accessing a server constructed on the network from a personal computer or a portable information terminal (hereinafter referred to simply as “information terminal”), the process of temporarily accessing a search site, which is an information search system on the network, and making a search for the information existing on the network by using the search engine is ordinarily performed. In the search site, natural language processing is ordinarily performed on information provided on the network to extract words as search keywords (hereinafter referred to simply as “keyword”), frequency information on the keywords and so on to construct a database. The search engine performs a search for information by searching the database and examining matching with an input keyword. The search engine also computes a score indicating the relation between the information found by the search in the database and the keyword by referring, for example, to the frequency information, and outputs search results ordered according to the obtained score.
Various devices have been made for search engines of this kind to perform information searches with efficiency. In recent years, information search methods utilizing an ontology used in Semantic Web techniques for handling semantics with a computer have also been proposed. The ontology is a knowledge notation method defined as a specification of a conceptualization or the like and used for semantic description of Semantic Web. On a system, it is implemented as a classification system and an inference rule set for example.
By using the ontology, a search based on a meaning can be introduced into a search in a database. That is, an information search is performed by considering a meaning attached to information on a network by means of the ontology. In this manner, the meaning of a keyword can be set as a search condition and only information in which words are used with the same meaning as that attached to the input keyword in formation containing the same words as those in the keyword can be searched for. Therefore, implementation of a method which enables a user to speedily obtain really necessary information for the user is expected.
For the conventional information search system, a method utilizing an ontology used in Semantic Web techniques has been proposed as a means for performing an information search with efficiency, as mentioned above.
However, even if a Semantic Web technique enables information on a network to have a meaning, there is a need to attach information for use of the ontology as a search condition as well as a keyword in order to search for information based on this meaning. That is, in a case where only keywords are input, only the keywords can be used as search conditions if a search is made without attaching information for use of the ontology. The search in this case is the same as ordinary search using only keywords without using the ontology.
For example, it is conceivable that in a case where a user searches for “Fujisawa de nichiyobi ni aiteiru haisha (a dental clinic open on Sunday in Fujisawa)” is searched for, he or she ordinarily inputs single words such as “haisha (dental clinic)”, “Fujisawa” and “nichiyo (Sunday)” as keywords. However, when a search is made by using only these keywords, full use of a meaning given to information on a network by Semantic Web cannot be made even if the meaning of each single word can be determined, because the relations between the single words are impaired.
On the other hand, it is necessary to describe an inquiry sentence in accordance with an ontology description language description form used on the network in order to give information for utilization of the ontology as a search condition. Thus, the user making the search is required to perform complicated operations.
Therefore, an object of the present invention is to provide a system which adds information for utilization of an ontology to search conditions without requiring a user to perform any complicated operations and thereby enables an information search making full use of meanings attached to information on a network by a Segmantic Web, and a method for such an information search.